An MRI device is a device to obtain a cross-sectional image representing a physical and chemical properties of a subject, using a nuclear magnetic resonance phenomenon that occurs when the subject is placed in a uniform static magnetic field and is irradiated with high frequency pulses, and is particularly used for medical purposes. An MRI device mainly includes a static-magnetic-field coil device for generating a uniform static magnetic field in an image capturing region where a subject is inserted, a gradient magnetic field coil for a generating gradient magnetic field in a pulse form to provide information on positions in the image capturing region wherein the strength of the gradient magnetic field has a spatial gradient, an RF coil for irradiating the subject with high frequency pulses, a receiving coil for receiving magnetic resonance signals from the subject, and a computer system for processing the received magnetic resonance signals and displaying a cross-sectional image as described above. FIG. 1 shows the outline of an MRI device. A magnetic field generated by a static-magnetic-field coil device 2 has a uniform magnetic field strength in an image capturing region 8 at the center of the device. A gradient magnetic field coil 3 generates a gradient magnetic field in this region. The central axis 10 is in parallel to the direction of the static magnetic field and is the symmetry axis of the static magnetic field coil of the MRI device. An affected part of a patient subject 5 is placed in the image capturing region 8 by moving a bed 6 or in another way.
For improving the performance of an MRI device, a gradient magnetic field coil for generating a gradient magnetic field whose magnetic field strength has a linear gradient have been proposed (refer to Patent Documents 1 to 3).